The invention relates to a novel operating scheme for enabling multiple processing environments in a single continuous flow completely mixed waste water treatment reactor system.
Controlling biological wastewater treatment processing in the chemical industry requires balancing many competing elements. The waste water of the chemical industry frequently contains high levels of organic carbon, ammonia and nitrates. Thus the treatment procedure may require the simultaneous removal of organic carbon, ammonia, nitrates and other priority pollutants.
Nitrification, the biological oxidation of ammonia to nitrates by autotrophic bacteria, is typically utilized to remove ammonia from waste water. This process thus generates additional nitrates as the ammonia is oxidized. These autotrophic bacteria generally use carbon dioxide as a carbon source during the nitrification reaction. The nitrification is a sensitive process and requires, for example, prescribed temperatures, a specific pH range, and an aerobic environment with a dissolved oxygen content of generally more than 2 mg O2/L. In addition, excessive amounts of inhibitory compounds such as salts, certain amines, and other compounds must be avoided. Another requirement is a long Solids Retention Time (SRT), which means a balance of moderate organic carbon levels in proportion to ammonia, to allow the slowly growing autotrophic bacteria to complete with the faster growing heterotrophic bacteria found in the waste water.
Denitrification, the biological reduction of nitrates to nitrogen gas with the utilization of the organic carbon waste by heterotrophic bacteria, is typically used to remove nitrates and organic carbons from the waste water. The primary requirements for denitrification include an anoxic environment with a dissolved oxygen content of less than 0.5 mg O2/L and adequate organic carbon substrate to balance the nitrate levels. Without adequate organic carbon, the heterotrophic bacteria can not reduce the nitrates. Thus, the dissolved oxygen requirements for nitrification and denitrification are mutually exclusive.
Several processes have been developed in an attempt to handle waste water having high levels of organic carbon, ammonia and nitrates using the nitrification and denitrification reactions. One process is a two sludge system that employs anoxic conditions with heterotrophic bacteria to consume organic carbon and reduce nitrates in a first bioreactor with solids recycling and a second independent bioreactor system under aerobic conditions to oxidize the ammonia. This process has the advantage of completely separating the nitrification and denitrification steps and is used where nitrates are present in the influent. The disadvantages of this process include a high capital cost and the inability to denitrify the nitrates generated in the nitrification step. This inability can be a significant problem when the level of ammonia in the influent is high.
Another process employs a single sludge system with two or more bioreactors. In this process, anoxic conditions are maintained in one vessel to facilitate denitrification while aerobic conditions are maintained in another vessel (or vessels) to facilitate nitrification. This arrangement is suitable to consume nitrates present in the influent waste water, but also suffers from an inability to denitrify the generated nitrates from the oxidation of ammonia. One way used to manage nitrification and denitrification in a single sludge process involves an internal recirculation step. This internal recirculation step is employed in the xe2x80x9cCarouselxe2x80x9d process, oxidation ditches and the Modified Ludzak-Ettinger (MLE) process. These processes function by creating different process conditions spatially within a single plug flow reactor, and recirculating generated nitrates from the aerobic zone to the anoxic zone. These modified methods are suitable for plug flow reactors treating waste water in which toxic overloads of chemicals are not an issue, but the methods cannot be adapted to a single vessel system. In many cases, these multiple vessel systems require very large piping and pumping systems, which are expensive to build and operate and may require system shutdown and major modifications. Because of the possibility of organic overload or toxic-inhibitory situations, most chemical industry wastewater treatment plants utilize completely mixed aeration basin systems.
Another process that is used is commonly known as a sequencing batch reactor (SBR). In a SBR a single vessel is employed for bioprocessing and solids separation. The system is not a continuous flow system, instead, waste water must be treated in batches. The SBR process is particularly useful for small municipal systems. This complete mixed single vessel can be adapted to nitrification and denitrification by creating anoxic and aerobic zones in the same vessel that are temporally separated, i.e., at different times during the batch cycle. One disadvantage of this process is the batch nature and an inability to adapt it to existing continuous flow systems. A further disadvantage is that it requires a separate system to store the waste water, which is continually produced, until it can be loaded into the batch reactor.
Thus, prior art processes can all be classified into two distinct groups. Continuous flow processes that maintain different physical zones for nitrification and denitrification. These processes are classified as spatially distinct. Batch processes that are not continuous flowing and that operate the entire system under uniform conditions, which vary between anoxic to aerobic at different times during the batch. These processes are classified as temporally distinct.
In general terms, this invention provides a single continuous flow completely mixed waste water treatment reactor system that is capable of multiple processing environments while maintaining continuous flow.
In one embodiment the present invention comprises a method for treating waste water comprising the steps of continuously flowing an influent into a treatment basin and continuously flowing an effluent out of the treatment basin into a clarifier. The method further comprises continuously completely mixing the influent in the treatment basin. In an additional step, oxygen is introduced into the basin for a first predetermined time period. The method further includes stopping the introduction of oxygen into the basin for a second predetermined time period and then repeating the steps of introducing and stopping the oxygen. In another embodiment the method further comprises introducing a supplemental source of carbon into the basin for a third predetermined time period, with the third predetermined time period being no greater than the second predetermined time period.
In another embodiment the present invention is a reactor system for treating waste water comprising: a treatment basin having an inlet for continuously receiving an influent stream, an outlet for continuously discharging an effluent stream, and containing a mixed liquor; at least one mixer, said at least one mixer completely and homogeneously mixing said mixed liquor; at least one source of oxygen, said at least one source of oxygen discharging oxygen into said mixed liquor; and a controller connected to said at least one source of oxygen, said controller cycling said at least one source of oxygen on and off.
The present invention offers several advantages over the prior art. The present invention demonstrates how an existing completely mixed reactor system can be modified to provide a continuously flowing reactor that is able to carry out both nitrification and denitrification. The system significantly reduces the level of nitrates in the influent and those generated within the reactor system itself. The present system enables the modification to be made at a reasonable cost. In addition, the system reduces the possibility of toxic levels of contaminates because the completely mixed continuous nature of the system rapidly dilutes contaminants. Finally, the present system removes the need to have influent storage tanks, which are often required with batch systems.
These and other features and advantages of this invention will become more apparent to those skilled in the art from the detailed description of a preferred embodiment. The drawing that accompanies the detailed description is described below.